The invention relates to an internal-combustion engine comprising a device for hydraulically adjusting the angle of rotation of the camshaft of the engine relative to the crankshaft of the engine, as well as to a vacuum pump for a servo load, especially for a brake booster.
For the person skilled in the art in the field of automotive technology, it is generally known that, in addition to a plurality of aggregate systems, modern internal-combustion engines are also equipped with a device for hydraulically adjusting the angle of rotation of the camshaft of the engine relative to the crankshaft of the engine, as well as with a vacuum pump for a servo load, in order, on one hand, to be able to continuously change the opening and closing valve timing of the gas-exchange valves of the internal-combustion engine with the device and, on the other hand, to generate with the vacuum pump the low pressure needed, for example, for a brake booster of a motor vehicle.
The typical devices for adjusting the angle of rotation are provided, in principle, as hydraulic actuators, which are configured either as so-called axial piston adjusters or as so-called rotary piston adjusters similar to the device known from EP 0 818 609 B1. This device is arranged on the drive-side end of the camshaft supported in several radial bearings in the cylinder head of the internal-combustion engine, and essentially consists of a drive unit connected in a driving manner to the crankshaft of the internal-combustion engine and a driven unit connected in a torsion-proof manner to the camshaft of the internal-combustion engine. The actual driven unit is provided as an impeller and fixed by an axial central screw to the camshaft, while the drive unit is provided as a hollow cylinder, which surrounds the driven unit and which can be sealed tight relative to a pressurizing medium by two axial side walls. Through four radial limiting walls in the drive unit and four radial vanes on the driven unit, two compression chambers, which can be pressurized alternately or simultaneously with a hydraulic pressurizing medium and via which the drive unit is connected in a force-transferring way to the driven unit, are then formed between two limiting walls within the device. Here, the lubricating oil fed from one of the radial bearings of the camshaft for the internal-combustion engine is used. This oil is supplied via radial and axial oil channels of the device as hydraulic pressurizing medium for the device.
In contrast, the vacuum pumps typically used in internal-combustion engines for a servo load are usually provided as vane pumps, like those that follow, for example, from DE 85 18 157 U1. This vacuum pump is arranged on a common longitudinal axis with the camshaft on the cylinder head of the internal-combustion engine, and essentially consists of a housing flanged to the cylinder head cover of the internal-combustion engine with a pillow block and a rotor arranged in the housing with a drive shaft, which is supported in a rotating manner in the pillow block of the housing projecting into the cylinder head of the internal-combustion engine. Here, two recesses, in which two coupling tabs formed on the end face of the camshaft engage, are machined into the end face of the drive shaft and thus the rotational movement of the camshaft is transferred to the drive shaft of the vacuum pump. In addition, the camshaft also has an axial lubricating oil channel, which leads to the end face of the camshaft and which is connected, on one side, via a coupling tube to an axial lubricating oil collection space in the drive shaft of the vacuum pump and, on the other side, to the lubricating oil circuit of the internal-combustion engine, so that the vacuum pump is simultaneously lubricated with the lubricating oil of the internal-combustion engine.
However, it has proven to be disadvantageous that for many engine designs, due to lack of space, there is no other economical option than to arrange the vacuum pump for the servo load opposite the drive-side end of the camshaft or one of the camshafts of the internal-combustion engine. However, if a device for hydraulically adjusting the angle of rotation is also provided on this end of the camshaft, then the driving and lubrication of the vacuum pump in the described manner via the camshaft of the internal-combustion engine is no longer possible, so that very expensive measures are usually necessary to realize the driving and lubrication of the vacuum pump in some other way. Here, primarily changing the vacuum pump in its structure must be taken into consideration, such that it can be integrated in a suitable way in the primary or secondary drive of the internal-combustion engine, as well as in the lubricating-oil circuit thereof, so that in each case, considerable extra expense for the internal-combustion engine must be taken into account.